There are systems, such as synchronous motors and generators, which supply electrical current to a rotor winding by way of slip rings. The current is typically applied to the slip rings via brushes mounted on a fixed conducting ring. Ordinarily, the slip rings in such systems are at low voltage. A prior art technique is to form the slip ring (usually copper in content) around the circumference of a rotating shaft of the rotor, e.g., by using epoxy to adhere or cast the slip ring to the shaft.
Some high voltage systems also employ slip rings for such purposes as power transfer. See, in this regard, U.S. Pat. No. 3,471,708 to Rauhut for a rotary transformer for coupling multiphase systems having a small frequency difference. But larger systems and high voltage systems introduce complications not present in low voltage systems, such as (for example) increased surface creepage area and thermal conditions.
In a high voltage system, both the rotatable shaft and the slip ring are susceptible to thermal expansion. However, the thermal expansion rates of the rotatable shaft and slip ring likely differ. For example, a steel rotatable shaft has a different (e.g., smaller) thermal expansion coefficient than a copper slip ring. Therefore, mounting the slip ring directly to the surface of a rotatable shaft can be problematic in a high voltage system.
What is needed, therefore, and an object of the present invention, is a high voltage electrical system which provides a suitable way of mounting a slip ring to a rotatable shaft.
An electrical current collector system includes a rotatable shaft; an electrically conductive slip ring; and slip ring support assembly. The slip ring support assembly comprises plural post insulators spaced angularly about the rotatable shaft for attaching the conductive slip ring to the rotatable shaft. The post insulators facilitate adjusting of the position of the slip ring relative to the rotatable shaft, e.g., to provide concentric positioning. The post insulators comprise an attachment/adjustment assembly for connecting to the slip ring. In one embodiment, the attachment/adjustment assembly comprises a spring plate which is adjustably biased to provide a preloading displacement that absorbs differential movement due to temperature changes of the slip ring and the rotatable shaft. In one example deployment, the current collector system is provided as part of a rotary transformer system which, e.g., transfers electrical power between a first electrical system (e.g., first electrical grid) and a second electrical system (e.g., second electrical grid).